Search the dictionary for _name_. If _name_ is found,
return TRUE; otherwise return FALSE. Immediate for use in
definitions.

[DEFINED] word ( -- nfa|0 ) immediate
does check for the word using find (so it does not throw like ' )
and puts it on stack. As it is immediate it does work in compile-mode
too, so it places its argument in the cs-stack then. This is most
useful with a directly following [IF] clause, so that sth. like
an [IFDEF] word can be simulated through [DEFINED] word [IF]